Band switching arrangement



Feb. 13, 1951 E. F. DE MERS BAND SWITCHING ARRANGEMENT Filed Dec. 17, 1947 INVENTOR Edward F. De Mers Aity.

Patented Feb. 13, 1951 g, 541,917 BANnswrrcmNGARRANG MENT- Edward E. De Mers, Urbana, 111. assignor to Stro nloerg-Carlson Company, a corporation of" ew. Ke k Application December. 17,1947, Serial No. 792,315-

3 Claims, (01. 171 24;)

The present inventionrelates. tea band switch ing arrangement; andmore particularly to an irnproved band switch a ang ml m' 9.13% with: a resonant frequency. varying. d i fi m lg aa a movable ferromagnetic 0.0 1

In recent years it has. become commonpractme to employ variableinductances in the tun ngc311:

cults ofwave signalreceivers, to perform the same function as the. variable. condensers commonly, employedin these circuits These variable in; ductances. oftenv form a part of circuits. for. example for usein Qscillators or other circuits which require resonant frequency var devices, and in which. Onefilement of the tank circuit comprises. a. fixed capacitor. Variations in inductive reactance areobtainedby changing the relative positions. of, a winding and moi epic coreformed of. a compressed, comminuted ferromagnetic material, often referred: to as. a po w dercd iron core.

It is, of course, desirable. that, a substantial change of inductance. occurs.- astherde iYQ .9 1? tions of the. winding and its. associated ferro; magnetic core are changed. 'Ijhe method of ing a. circuit by changing the relativeposition of such. a ferromagnetic, core and any associajt d winding is ccmmonlycalledpermeability tuning,

It is a well known fact. that the resonant fre: quency. of. a circuittuned to parallel resonance may be expressedby the followingequation;

,= ah/7T where f is they frequency inmegacycles per, second, L is the inductance inmicrohenrys. and C is the capacitance in microfarads. By varying the value of theinductance L while permitting the value of the capacitanceC to remain, constant, the resonant frequency f is. varied. From. the aboveequationit is clear. that the frequencvvari inversely as the. square. root of. the inductance and consequently-if. theinductance changes by a factor ofnine. the. resonant frequency, which it isdesired to vary-will changeonly byafactor of three.

Unfortunately, ordinary variable .inductanccs v0. the movableferromagnetic core type. do not provide a sufficientchangein.inductancetc provide the wide ranges of resonant frequencyvariation required in modern. wave signal receivers, which receivers may be capable of receiving signalsin the standard broadcast band, the short wave band, and. the frequency modulationv band-tin fact: in some cases even including the television a c d n l t s. be nc mqc i c to employ. plurality of separate tuned circuits,

one for each band, with selectively operable band switching means for rendering the proper tuned. circuit effectivewhenit isdesiredto tunein a sigjnal within the associated band. As a matterlof fact inconventional permeability tunedreceivers the 7 resonant frequency increases approximately by, a; factor of three asthe ferromagnetic core.

moves from the coreralleinf position to the.

core-all-outi position. For thestandard broadcast-band this has been veryadequate since the frequency range of the standard broadcastband g ne al y. xt n s r m; fi 1 c Q es t 0 lgilocycles. It would be desirable to provide a variable inductance which coul d. be employedv in connection with tuned circuits whereby'the resonant frequency may changesby, a factor substantially greater than three without the requireme t f d iiienat n t imii i Qrihe e;

Accordingly, it is, an object of the present in: ventiontoprovidea new and improved resonant r que eryine cc wher by a w range of. resonant frequencies may. be obtained in a relat v lv im e mann It. is anotherjobject' or the. present invention to provide a newand improved variable.induct ance of the; type employing a. movable ferromagnetic core in] which a very wide range. of inductive. reactance is obtainable, in a simple nd. ne n iv e ne i Still another object of the present invention is. v to provide: a new and improved permeability tuned circuit in which band switching may be obtained in a simplemanner using the same coil and the identical capacitance for a plurality of different bands. 7'

Further objects andadvantages of the present invention willbecome apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularityin the claims annexed to and forming a partofathis specification. i

For a better understanding er. the present invention reference-may behad to the accompanying drawing, in which} I Fig. 1 is a schematic diagram of a circuit which may be employed in a wave signal receiver which comprises a resonant. frequency varying device including the band switching arrangement of the present invention shown in the position for receiving the low frequency band.

Fig. 2 is a perspective view of a variable inductance comprising a movable ferromagnetic core such as is schematically shown in Fig. 1.

Fig. 3 is a perspective view of a switching mechanism for performing a band switching operation on the resonant frequency varying device of Fig 1 and Fig. 4 is a schematic diagram of a portion of Fig. 1, showing the other switching position of the band switching arrangement not shown in Fig. 1 of the drawing, or in other words, showing the position of the band switching arrangement for receiving the high frequency band.

Although the present invention is broadly concerned with a variable inductance, it is particularly applicable to resonant frequency varying; devices employed in modern wave signal receivers. Accordingly, and by way of example only, the present invention has been illustrated as applied to such resonant frequency varying circuits, but it should be understood that it may be applicable to other fields.

Referring now to Fig. 1 of the drawing, there is illustrated a tuned circuit, generally indicated at 9, comprising a capacitor I!) of relatively fixed capacitive reactance and an inductance generally indicated at ll capable of providing a selectively variable inductive reactance.

I As is best shown in Fig. 2 of the drawing, the variable inductance II comprises a suitable coil support I2, illustrated as a tubular insulating member for receiving therewithin a movable ferromagnetic core I3 preferably formed of a compressed comminuted ferromagnetic material such as powdered iron or the like. The core i3 preferably is provided with a threaded extension [3a which may be connected to suitable means for moving the core [3. For the purpose of suitably mounting the coil support I2 there is provided a strip-like member I4 preferably formed of an insulating material. Any suitable means for rigidily interrelating the coil support I2 and the strip-like member I4 in the manner shown in Fig. 2 of the drawing may be employed. The tubular coil support I2 has suitably wound thereon a coil generally designated at l5, which, as illustrated in Fig. l of the drawing, comprises three separate windings 5a, I51; and 5c, each wound on the tubular coil support If so that if the windings are connected in parallel they tend to produce mutually aiding magnetic fluxes. The ends of each of the winding sections 55a, l5s and his of the coil are connected to suitable terminals I6a-l6'a, I6b-l6'b and I6cI6c, respectively, which terminals are illustrated as being suitably mounted on the strip-like member I I in a predetermined manner to be described hereinafter.

It will be understood that the tuned circuit 9, the resonant frequency of which may be selectively varied by movement of the ferromagnetic core I3, may be employed in various circuits. In Fig. l the tuned circuit 9 is illustrated as being employed in an oscillator circuit which may comprise one stage of a superheterodyne type of wave signal receiver. As illustrated in Fig. 1 of the drawing, the tank circuit 9 has one terminal thereof connected to the anode or plate ii of an electron discharge valve 13, illustrated as a triode, through a coupling capacitor I9. The electron discharge valve I8 further comprises a cathode 20 and a grid or control electrode 2!. The cathode Is is illustrated as being connected to ground generally indicated at 22. The other terminal of the tank circuit 9 is connected to the control electrode 2i through a suitable coupling.

capacitor 23. A grid leak resistor 24 is indicated as connected between the control electrode 2| and ground 22. The plate ll of the triode i3 is also connected to a source 25 of +B potential through a choke coil 27. It will be understood that by changing the position of the ferromagnetic core E3 of the variable inductance II relative to the 4 coil I5 the resonant frequency of the tank circuit 9 may be selectively changed so that the frequency of the output signal of the oscillator circuit shown in Fig. 1 of the drawing may also be selectively changed.

As was mentioned above, the resonant frequency of a tuned circuit of the type disclosed at 9 in Fig. 1 of the drawing increases substantially by a factor of three while the core I3 is moved from the core-allin position to the coreall-out position. This means that for this range the inductance must change inversely by a factor of nine. In accordance with the present invention the three windings [58,, I51, and I50 of the coil I5 are arranged to be selectively connected either in series or in parallel. When the windings are connected in series, the inductive reactance of the coil I5 has been found to be approximately nine times larger for the same core position as when the three windings are connected in parallel. In other words when the windings I5a, |5b and I50 are connected in parallel and the core I3 is in the core-all-in position the inductive reactance of the coil I5 is substantially the same as when the windings I511, His and 5c are connected in series and the core I3 is in the core-all-out position. Consequently, the inductance of the coil may be controlled over two contiguous frequency bands thereby providing a resonant frequency range substantially twice that of conventional permeability tuned circuits.

Any suitable mechanism may be provided for selectively connecting the winding sections 15a, '51) and 5c of the coil I5 either in series or in parallel. As illustrated the terminals [8a, is, Ific, :S'a, It's and IGc are arranged in that order on the strip-like member [4 with a predetermined spacing therebetween. The terminals as, and It's are spaced a substantial distance from the adjacent terminals I611 and It's respectively. The terminals IEb and 6c and lfis and 15's are spaced relatively close together with a substantial distance between the terminals Ito and Iiia, this distance actually being the same as the spacing between the end terminals I63 and ISc and the adjacent terminals I61 and It's respectively. By employing this particular spacing of the terminals IS a pair of switching members specifically designated as 3i and 32 in the drawing which are identical in construction may be employed. I'he movable switching members 3| and 32 are provided with suitable contacting portions so that when in the position shown in Fig. l of the drawing the winding sections I511, I5b and I5 are connected in series while when in the position shown in Fig. 4 of the drawing the winding sections I511, I51, and i5c are connected in parallel.

As illustrated the switching member 3| is provided with a plurality of spaced contact means 3|a, 3h; and 3Ic. These spaced contact means are positioned in a predetermined manner relative to the spacing of the terminals l6 so that when the movable switching element 3| is in the position shown in Fig. 1 of the drawing the contact portion 3'5. engages terminal '60 while the contact portion 3Ic engages terminal It's. The contact portion He does not engage any contact in this position of the switching member 3!. In the other position of the switching element 3| shown in Fig. 4 of the drawing the contacting portions 3'31, 3Ib and 3 lo of the switching element 3I engage terminals I6a, [6's and I3c, respectively, thereby connecting in parallel the corresponding ends of the winding sections '59., |5b and. 5c.

The switching element 32 is provided with identical contact portions 32a, 32b and 32. In the position shown in Fig. 1 of the drawing the contact portion 329, is in engagement with the terminal 6's. while the contact portion 32c is in contacting engagement with the terminal Hit. The contact portion 32b does not engage any contact in this position of the switching member 32. It will be apparent that in this Fig. 1 position of the switching elements 3! and 32 the winding sections of the coil [5 are connected in series relationship. In the other position of the switching element 32 shown in Fig. 4 of the drawing the contacting portions 320, 32b and 32a are adapted to engage with the terminals Ilia, 15b and I60 respectively, thereby connecting in parallel the other ends of the winding sections of the coil I5.

It will be understood that simultaneous movement of the switching elements 3| and 32 should occur so that the elements are in either of the two positions shown in Figs. 1 and 4 of the drawing. Any suitable means for producing such simultaneous movement may be provided. In Fig. 3 one such means is illustrated in which the switching elements 3| and 32 are provided along their adjacent parallel surfaces with teeth so as to define rack portions 31 and 38. A suitable gear 39, preferably formed of some insulating material and mounted on a suitable shaft 40, is adapted simultaneously to engage with the rack portions 31 and 38. The rack portions 31 and 38 and the gear 39 will be so designed that movement of the switching elements from the position shown in Fig. 1 to the position shown in Fig. 4 of the drawing is accomplished with less than 360 rotation of the gear 39. If desired the shaft 40 may be provided with a suitable manually engageable knob 4| having a pointer 42 thereon for cooperating with suitable indicia such as band A and band B indicating the two band switching positions.

In order to limit the extreme positions of the switching elements 31 and 32 suitable stop elements such as 44 and 45 may be provided. As illustrated the stop elements 44 and 45 are adapted to limit the movement in either direction of the switching element 32, this element being shown against the stop 44 in Fig. 1 of the drawing and against the stop 45 in Fig. 4 of the drawing.

In view of the detailed description included above the operation of the permeability tuning device of the present invention incorporating the band switching element will be understood by those skilled in the art. By a simple switching mechanism the winding sections l5a, l5b and 15c of the coil IS with which the movable ferromagnetic core I3 is associated may be connected either in series or in parallel. When connected in series the tuning circuit operates in the lower frequency band and when connected in parallel the tuned circuit operates in the higher frequency band. As has been mentioned above these frequency bands are adjacent or contiguous bands with the high frequency point on the low frequency band corresponding substantially to the low frequency point on the high frequency band.

Although there has been illustrated a specific embodiment of the present invention, it should be understood that various modifications will occur to those skilled in the art. Accordingly it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the present invention.

What is desired to be secured by Letters Patent of the United States is:

l. A resonant frequency varying device comprising a variable inductance including an insulating tube, a terminal board associated with said tube, a coil comprising a plurality of parallel conductors wound on said tube, a plurality of pairs of terminals one pair for each of said conductors mounted in spaced relationshi on said terminal board, means for connecting the ends of each conductor wound on said tube to the associated pair of terminals, switching means associated with said terminals for controlling the connections of said windings so that when said switching means is in one position said conductors are connected in series, and when said switching means is in another position said condoctors are connected in parallel, and a ferromagnetic core disposed within said tube and movable along the axis for varying the resonant frequency of said device.

2. A resonant frequency varying device comprising a variable inductance including an insulating tube, a terminal board associated with said tube, a coil comprising a plurality of parallel conductors wound on said tube, a plurality of pairs of terminals one pair for each of said conductors mounted in spaced relationship on said terminal board, means for connecting the ends of each conductor wound on said tube to the associated pair of terminals, switching means associated with said terminals for controlling the connections of said windings so that when said switching means is in one position said conductors are connected in series, and when said switching means is in another position said conductors are connected in parallel, a ferromagnetic core disposed within said tube and movable along the axis for varying the resonant frequency of said device, and means for limiting the movement in each direction of said switching means.

3. A resonant frequency varying device comprising a variable inductance including an insulating tube, a coil comprising a plurality of parallel conductors wound on said tube, a plurality of pairs of terminals, one pair for each of said conductors, means for connecting the ends of each conductor wound on said tube to the associated pair of terminals, switching means associated with said terminals for controlling the connections of said windings so that when said switching means is in one position said conductors are connected in series, and when said switching means is in another position said conductors are connected in parallel, and a ferromagnetic core disposed within said tube and movable along the axis for varying the resonant frequency of said device.

EDWARD 13''. DE LEERS.

REFERENCES CITED The following references are of record in the :file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Australia May 20, 1937 Number Number 

